There are two common ways to magnetically detect the presence of a vehicle. The first way uses what is known as a loop sensor, which inductively couples with the vehicle as it passes near the loop sensor, producing an induced current in the electrical loop. This induced current is measured, possibly after being amplified. Detection of vehicular motion proceeds by analyzing this measured signal from the loop sensor. The second way uses a magneto-resistive sensor, whose internal resistance changes due to fluctuations in the magnetic field it experiences. Often the resistance is determined by measuring a voltage drop across the sensor. These measurements are used to determine the starting and ending time for a vehicle passing near the magnetic sensor. The signals from these sensors vary greatly, making determining the starting and ending times very erratic. Typically these measured signals are analyzed in terms of their rate of change, which often worsens the effect of noise.
What is needed is a method and supporting apparatus, which can use the raw signal from a magneto-resistive sensor to reliably capture the start time and the ending time for a vehicle passing near the magnetic sensor.